Japanese Patent Application No. H11-160759 discloses a parallel type hybrid system which comprises: an engine, a transmission device for changing the speed of rotation of an input shaft and transmitting said rotation to vehicle wheels via an output shaft, a clutch for engaging/ disengaging the output shaft of the engine with/from the input shaft of the transmission device, a rotational electric device serving as an electric motor and an electric generator, a power transmission mechanism for coupling the input and output shafts of the rotational electric device with the input shaft of the transmission device, and an accumulator element for accumulating electrical power supplied by the rotational electric device.
In prior applications of this kind, it can be seen that the friction and inertia of the rotational electric device acts via the power transmission mechanism on the input shaft of the transmission device, thereby placing a great load on the synchronous mechanism when changing gear, and increasing the gear changing time (synchronous time).